1. Field of the Invention
The present invention relates to a filter apparatus for an electronic musical instrument, which generates various musical tone waveforms.
2. Prior Art
Conventionally, as electronic musical instrument generates musical tones having characteristics of acoustic musical tone, such that the tone color of the musical tone is altered by a filter which has a variable frequency characteristic. The first conventional musical tone generating apparatus is disclosed in Japanese Utility model laid-Open Publication No. Sho52-34092 shown in FIG. 14. In FIG. 14, the musical tones from tone source 4 are supplied to tone color controllers 5a, 5b and 5c, and open-close circuits 3a, 3b and 3c through key-switch SW1, SW2 and SW3. Each tone color controller 5a, 5b and 5c adds tone color parameters to each musical tone which is inputted therein, and outputs each musical tone to amplifier AMP, as a first musical tone. Each open-close circuit 3a, 3b and 3c outputs the musical tone which is inputted therein, to tone color controllers 5d, 5e and 5f according to the envelope from envelope circuit 2. Each tone color controller 5d, 5e and 5f adds tone color parameters to each musical tone which is inputted therein, and outputs each musical tone to the amplifier AMP, as a second musical tone. In the amplifier AMP, the first musical tone and the second musical tone are mixed, and then the mixed musical tone is outputted from speak SP as musical sound.
However, in the above-mentioned conventional apparatus shown in FIG. 14, while it is possible to change the frequency characteristic of the tone color controllers 5a, 5b, 5c, 5d, 5e, it is impossible to control a rate of change the envelope in accordance with a state of the touch information (key-on velocity, key-off velocity and so on) of the keyboard 1.
Hence, in this first conventional apparatus, only a musical tone having simple tone color is obtained.
Next, the second conventional musical tone generating apparatus is disclosed in U.S. Pat. No. 4,843,938 shown in FIG. 15. In FIG. 15, plural filter parameters which designate frequency characteristic of a digital-filter 7, which is used as a tone color controller, are memorized in a memory 8, and are supplied to the digital-filter 7 according to touch information from a keyboard 1, in each fixed interval (frame). Therefore, a musical tone from a waveform memory 9 is filtered by the digital-filter 7 having frequency characteristic which changes with elapsed time. As a result, the envelope of the musical tone changes variably in accordance with frequency characteristics. This musical tone is supplied to the D/A converter 10, and outputted as musical sound by sound system SD.
In the apparatus shown in FIG. 15, if it is desired to change the rate of change of the frequency characteristic of the digital-filter, the apparatus must be expanded such that it would be necessary to provide a means which changes the outputting velocity of the filter parameter, or to provide a larger memory in which plural filter parameters designating various changes of performance information are memorized.